1. Field of the Invention
The present invention relates to a bolt and a semiconductor manufacturing apparatus, particularly to a bolt used preferably for a wafer holding device holding a wafer, to which an ion beam is irradiated, and a semiconductor manufacturing apparatus processing a wafer by irradiating an ion beam thereto.
2. Description of the Related Art
One of important steps of manufacturing a semiconductor device is a step of doping a semiconductor material with a small amount of a chemical element. Ion implantation is known as a method of doping a semiconductor wafer with dopant atoms. The ion implantation is a technique for doping the semiconductor wafer by ionizing the dopant atoms, accelerating the ionized atoms to form an ion beam with a necessary energy and irradiating the ion beam to a front surface of the wafer. The ionized atom repeats collision with constituent atoms of the semiconductor crystal and finally stops in the crystal.
In the ion implantation, insufficient grounding of the wafer causes electrification of the wafer resulting in uneven irradiation of the ion beam to the front surface of the wafer. As the result, the uniformity of the dopant distribution within the wafer surface becomes worse to cause a quality degradation and a yield loss of the semiconductor device.
Japanese Laid Open Patent Application (JP-A-Heisei 7-180053) discloses a conventional wafer holding device, which discharges electric charges from a back surface of a wafer to a base.
FIGS. 1 and 2 show the wafer holding device according to the Japanese Laid Open Patent Application (JP-A-Heisei 7-180053). FIG. 1 shows a sectional view of the wafer holding device holding a wafer 400. FIG. 2 shows a plan view of the wafer holding device. In FIG. 2, the wafer 400 is omitted. The wafer holding device is installed in a semiconductor manufacturing apparatus.
In general, an insulation film such as a photoresist or an insulating oxide is formed on a front surface of the wafer 400 and, thus, the wafer 400 cannot be grounded via a damper 403 pressing a peripheral portion of the wafer 400 to a base 401. In addition, a rubber-like elastic body 402 contacting with the back surface of the wafer 400 is dielectric and, hence, the wafer 400 cannot be grounded via the rubber-like elastic body 402.
Therefore, in such a wafer holding device, a discharging pass is formed by installing a pin 404, a spring 405 and a lid 406 of electrically conductive materials in the base 401, by making a through-hole 402a in the rubber-like elastic body 402 and by pressurizing the pin 404 with the spring 405 to the back surface of the wafer 400 to make a contact between the pin 404 and the back surface.
When sliding portions of the pin 404 and the spring 405 are deteriorated to cause awkward movement of the pin 404 and when the surfaces of the pin 404 and the spring 405 are stained to increase a contact resistance between the pin 404 and the spring 405, the pin 404 and the spring 405 should be replaced by new ones.
However, when the pin 404 and the spring 405 are replaced, it is necessary to remove the lid 406 from the base 401 for removing the old pin 404 and spring 405 and to mount a new pin and spring on the base 401 followed by attaching the lid 406 to the base 401. Thus, many steps are required for the replacement.
Particularly, when the pin 404 and the spring 405 cannot be replaced in the state where the base 401 is fixed to a shaft of a motor for rotating the wafer holding device, the step of removing once the base from and attaching again to the shaft is necessary and, hence, a period for which the semiconductor manufacturing apparatus cannot be used becomes longer.